Bicycle rear derailleur

ABSTRACT

A bicycle rear derailleur includes a base member, a movable member, a linkage and a motor unit. The base member is configured to be mounted to a bicycle. The movable member is movably coupled to the base member. The linkage includes an outer link pivotally connected to the base member about a first pivot axis and pivotally connected to the movable member about a second pivot axis, and an inner link pivotally connected the base member and the movable member. The motor unit includes an output shaft having a rotational axis being parallel to one of the first pivot axis and the second pivot axis. The output shaft of the motor unit drives the outer link to move the movable member with respect to the base member. The inner link moves in response to movement of the outer link.

BACKGROUND

1. Field of the Invention

This invention generally relates to a bicycle rear derailleur. Morespecifically, the present invention relates to a bicycle rear derailleurhaving a linkage moved by a motor unit.

2. Background Information

A bicycle typically uses a chain drive transmission for transmitting apedaling force to a rear wheel. The chain drive transmission of abicycle often uses derailleurs to selectively move a chain from one of aplurality of sprockets to another for changing speeds of the bicycle. Atypical derailleur has a base member, a movable member supporting achain guide and a linkage assembly (e.g., a moving mechanism) coupledbetween the base member and the movable member so that the chain guidemoves laterally relative to the base member. Recently, derailleurs havebeen equipped with motor units to make shifting gears easier.

SUMMARY

Generally, the present disclosure discloses various features of abicycle derailleur. In one feature, a bicycle rear derailleur isprovided that includes a linkage and a motor unit that provides acompact arrangement.

In view of the state of the known technology, a bicycle rear derailleuris provided that basically comprises a base member, a movable member, alinkage and a motor unit. The base member is configured to be mounted toa bicycle, The movable member is movably coupled to the base member. Thelinkage includes an outer link pivotally connected to the base memberabout a first pivot axis and pivotally connected to the movable memberabout a second pivot axis, and an inner link pivotally connected thebase member and the movable member. The motor unit includes an outputshaft having a rotational axis being parallel to one of the first pivotaxis and the second pivot axis. The output shaft of the motor unitdrives the outer link to move the movable member with respect to thebase member. The inner link moves in response to movement of the outerlink.

Other objects, features, aspects and advantages of the disclosed bicyclerear derailleur will become apparent to those skilled in the art fromthe following detailed description, which, taken in conjunction with theannexed drawings, discloses one embodiment of the bicycle rearderailleur.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a partial side elevational view of a rear portion of a bicyclewith a bicycle rear derailleur in a low operating position;

FIG. 2 is a frame side perspective view of the rear derailleurillustrated in FIG. 1 with the rear derailleur in the low operatingposition when a chain is not engaged;

FIG. 3 is a partial side elevational view of a rear portion of a bicyclewith a rear derailleur in a low operating position when a cover memberof the movable member is detached;

FIG. 4 is a cross sectional view of a rear portion of a bicycle with arear derailleur in a low operating position;

FIG. 5 is a frame side perspective view of selected parts of the rearderailleur of FIGS. 1 and 2 with the rear derailleur in the lowoperating position;

FIG. 6 is a frame side perspective view of selected parts of the rearderailleur of FIGS. 1 and 2 with the rear derailleur moved from the lowoperating position of FIG. 5 to an intermediate operating position;

FIG. 7 is a frame side perspective view of the selected parts of therear derailleur of FIG. 6 with the saver mechanism in a first non-drivetransmitting position;

FIG. 8 is a frame side perspective view of the selected parts of therear derailleur of FIG. 6 with the saver mechanism in a second non-drivetransmitting position;

FIG. 9 is a top plan view of selected parts of the rear derailleur ofFIGS. 1 and 2 showing the base member supporting the motor unit and theouter link operatively coupled to the motor unit via the savermechanism;

FIG. 10 is a top plan view of selected parts of the rear derailleur ofFIGS. 1 and 2 showing internal components of the motor unit;

FIG. 11 is a frame side perspective view of the selected parts of therear derailleur of FIGS. 1 and 5 showing the motor unit and the outerlink operatively coupled to the motor unit via the saver mechanism;

FIG. 12 is a frame side perspective view of the motor unit, the outerlink and the saver mechanism of the rear derailleur of FIGS. 1 and 2,but with the drive link removed;

FIG. 13 is another frame side view of the motor unit, the outer link andthe saver mechanism of the rear derailleur of FIGS. 1 and 2, but withthe drive link removed;

FIG. 14 is a frame side view, similar to FIG. 13, of the motor unit, theouter link and the saver mechanism of the rear derailleur of FIGS. 1 and2, but with outer link moved to the top operating position;

FIG. 15 is a frame side view of the selected parts of the rearderailleur of FIG. 6 with the saver mechanism in the first non-drivetransmitting position; and

FIG. 16 is a frame side view of the selected parts of the rearderailleur of FIG. 6 with the saver mechanism in the second non-drivetransmitting position.

DETAILED DESCRIPTION OF EMBODIMENTS

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the art from thisdisclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

Referring initially to FIG. 1, a rear portion of a bicycle 10 isillustrated that includes, among other things, a bicycle rear derailleur12 in accordance with an illustrated embodiment. The rear derailleur 12is secured to a rear portion of a bicycle frame 14 in a conventionalmanner as discussed below. The rear derailleur 12 is operated by anelectric rear shifter (not shown), which is a shift actuating device.The electric rear shifter operates the rear derailleur 12 between aplurality of shift stage (gear) positions such that a chain 16 is movedby the rear derailleur 12 in a lateral direction between a plurality ofrear sprockets S. The rear derailleur 12 is illustrated in a low shiftstage (gear) position in FIG. 1. As used herein, the term “low shiftstage (gear) position” refers to the rear derailleur 12 being in anoperating that corresponds to the chain 16 being guided onto the rearsprocket S with the largest number of teeth. As used herein, the term“top shift stage (gear) position” refers to the rear derailleur 112being in an operating position that corresponds to the chain 16 beingguided onto the rear sprocket S with the smallest number of teeth.

The bicycle rear derailleur 12 basically includes a base member 18, amovable member 20 and a linkage 22. A motor unit 24 is operativelycoupled to the linkage 22 to move the movable member 20 with respect tothe base member 18. Thus, in the illustrated embodiment, the rearderailleur 12 constitutes an electric or motorized rear derailleur. Asaver mechanism 26 operatively couples the motor unit 24 to the linkage22 to provide protection for the motor unit 24 as discussed below.

In the illustrated embodiment, the base member 18 includes a firstbracket member 28, a second bracket member 30 and a bracket axle unit32. The first and second bracket members 28 and 30 are preferablyconstructed of a hard rigid material such as a lightweight metal (e.g.,an aluminum alloy). The first and second bracket members 28 and 30 arefixed together by a pair of bolts 34. The motor unit 24 is supportedbetween the first and second bracket members 28 and 30 with one of thebolts 34 passing through the motor unit 24 to secure the motor unit 24to the base member 18. As seen in FIG. 2, the first bracket member 28also includes a low shift stage adjustment screw 36 a and a top shiftstage adjustment screw 36 b for setting range of movement of the movablemember 20 with respect to the base member 18. The bracket axle unit 32is attached to the first bracket member 28 by a bolt 38. The bracketaxle unit 32 includes a fixing bolt 40. The fixing bolt 40 is threadedinto a threaded hole of the bicycle frame 14. Thus, the base member 118is configured to be mounted to the bicycle 10 by the fixing bolt 40.

As seen in FIGS. 1 to 3, the movable member 20 is movably coupled to thebase member 18 by the linkage 22. The movable member 20 includes a chainguide 42 pivotally coupled to the movable member 20 by an axle 44 topivot about a chain guide pivot axis P, which is sometimes called theP-axis of the rear derailleur. The axle 44 is made of several pieces(not shown) to aid in the assembly of the movable member 20 and theattachment of the chain guide 42 to the movable member 20.

As best seen in FIGS. 2 and 3, the chain guide 42 basically includes apair of chain cage plates 46, a tension pulley 48 and the guide pulley50 rotatably disposed between the chain cage plates 46. In theillustrated embodiment, the guide pulley 50 is rotatably disposed on theaxle 44, while the chain guide 42 is non-rotatably mounted to the axle44. As seen in FIG. 4, a biasing element 52 is provided between themovable member 20 and the chain guide 42 to bias the chain guide 42around the chain guide pivot axis P in a first rotational direction D1.Thus, the first rotational direction D1 is a clockwise rotationaldirection of the chain guide 42 around the chain guide pivot axis Pwhile being viewed along the chain guide pivot axis P from the non-framefacing side of the movable member 20. In this illustrated embodiment,the biasing element 52 is a torsion spring having a coiled portiondisposed around the axle 44, a first spring end engaged with the movablemember 20 and a second spring end engaged with the chain guide 42.

In the illustrated embodiment, the movable member 20 is provided with afriction element 54 operatively arranged between the movable member 20and the chain guide 42 to frictionally provide rotational resistance ina second rotational direction D2 of the chain guide 42 about the chainguide pivot axis P. Preferably, friction element 54 is adjustable tovary the rotational resistance provided by the friction element 54.Basically, the friction element 54 increases an operation energy of themotor unit 24 as the motor unit 24 moves the movable member 20 towardthe low shift stage position with respect to the base member 18. Thefriction element 54 constitutes a resistance applying element. In thisillustrated embodiment, a one-way clutch 56 is disposed between thefriction element 54 and the axle 44. The friction element 54 appliesresistance to the rotational movement of the chain guide 42 in thesecond rotational direction D2 with respect to the movable member 20. Inparticular, the friction element 54 applies frictional resistance torotational movement of the chain guide 42 by applying frictionalresistance to the rotation of one-way clutch 56. Since resistanceapplying elements and one-way clutches similar to the friction element54 and the one-way clutch 56 are discussed in detail in U.S. PatentApplication Publication No. 2012/0083371, the friction element 54 andthe one-way clutch 56 will not be discussed in further detail herein.

The linkage 22 operatively connects the movable member 20 to the basemember 18. In the illustrated embodiment, the linkage 22 includes afirst or outer link 60 and a second or inner link 62. The outer link 60is pivotally connected to the base member 18 by an output shaft 64 ofthe motor unit 24 about a first pivot axis A1. The outer link 60 ispivotally connected to the movable member 20 by a pivot pin 66 about asecond pivot axis A2. The inner link 62 is pivotally connected the basemember 18 by a pivot pin 68 about a third pivot axis A3 and the movablemember 20 by a pivot pin 70 about a fourth pivot axis A4. Thus, theouter and inner links 60 and 62 have first ends pivotally connected tothe base member 18 and second ends pivotally connected to the movablemember 20 to define a four bar linkage arrangement.

As seen in FIG. 2, the linkage 22 further includes a biasing member 72that is interposed between the outer and inner links 60 and 62 to biasthe movable member 20 towards one of a low shift stage position and atop shift stage position. In the illustrated embodiment, the biasingmember 72 is a coil tension spring that biases the movable member 20towards the low shift stage position. In particular, the biasing member72 has a first end 72 a connected to the outer link 60 by a firstmounting element 74 (e.g., a screw as shown, a press-fitted pin or othersuitable mounting element) and a second end 72 b connected to the innerlink 62 by a second mounting element 76 (e.g., a screw as shown, apress-fitted pin or other suitable mounting element), With thisarrangement, the biasing member 72 is stretched as the movable member 20moves from the low shift stage position to the top shift stage position.In the low shift stage position, the biasing member 72 is preloaded(slightly stretched) so that the outer link 60 contacts a tip of a lowshift stage adjustment screw 36 a as seen in FIG. 2.

The biasing member 72 aids in taking up play or clearance between thegears of the motor unit 24 and other manufacturing tolerances in themanufacture of the rear derailleur 12. As a result, when the motor unit24 is operated in a first rotational amount from a first position to asecond position, and then the motor unit 24 is subsequently operated ina second rotational amount from the second position to the firstposition, the first and second rotational amounts may become slightlydifferent position if the biasing member 72 is not provided to bias themovable member 22 in one direction. Thus, the biasing member 72 improvesthe stability of the shift positions of the rear derailleur 12.

In the illustrated embodiment, the outer link 60 includes a firstlinking member 80 and a second linking member 82, but the outer link 60may be made by a single piece, if needed and/or desired. A first end 80a of the first linking member 80 is pivotally connected to the basemember 18 by a first end of the output shaft 64 of the motor unit 24about the first pivot axis A1. Specifically, the first end 80 a of thefirst linking member 80 is not fixed to the output shaft 64, but ratherthe output shaft 64 can rotate relative to the first end 80 a of thefirst linking member 80. The second linking member 82 is rotatablymounted on a second end of the output shaft 64 of the motor unit 24.When assembling the rear derailleur 12, it is easy to attach the outerlink 60 to the output shaft 64 of the motor unit 24 as pivot shaft ofthe outer link 60 because the outer link 60 constructed by a pluralparts. A second end 80 b of the first linking member 80 is pivotallyconnected to the movable member 2.0 by the pivot pin 66 about the secondpivot axis A2. A first end 82 a of the second linking member 82 ispivotally connected to the base member 18 by the output shaft 64 of themotor unit 24 about the first pivot axis A1. Specifically, the first end82 a of the second linking member 82 is not fixed to the output shaft64, but rather the output shaft 64 can rotate relative to the first end82 a of the second linking member 82. A second end 82 b of the secondlinking member 82 is fixedly attached to an intermediate portion 80 c ofthe first linking member 80 by the mounting element 74.

Now the motor unit 24 will be discussed in more detail. The motor unit24 includes a motor 84, a gear reduction unit 86 and a shift stageposition sensor 88. The motor 84, the gear reduction unit 86 and theshift stage position sensor 88 are disposed inside a motor housing 90that is supported on the base member 18. The motor 84 is a reversibleelectric motor. Rotation of the output shaft 64 in one direction movesthe movable member 20 and the chain guide 42 toward a low shift stageposition with respect to the base member 18, and that rotation of theoutput shaft 64 in the other direction moves the movable member 20 andthe chain guide 42 toward a top shift stage position with respect to thebase member 18. The output shaft 64 of the motor unit 24 is connected toan output shaft 84 a of the motor 84 by the gear reduction unit 86. Theoutput shaft 64 of the motor unit 24 is connected the outer link 60 bythe saver mechanism 26 as discussed below. In the illustratedembodiment, the shift stage position sensor 88 is a digital positionsensor that this mounted on the gear reduction unit 86 to detectmovement of one of the parts of the gear reduction unit 86. Moreparticularly, the shift stage position sensor 88 of the illustratedembodiment is formed by a position sensor shutter wheel and a dualchannel photo interrupter having a light source or LED that is disposedon one side of the shutter wheel and a phototransistor (e.g., a lightdetector) disposed on the other side of the shutter wheel.

The output shaft 64 of the motor unit 24 is rotatably mounted to withinmotor housing 90 to project out of opposite ends of the motor housing 90to pivotally support the outer link 60 on the base member 18. The outputshaft 64 of the motor unit 24 has a rotational axis R that is parallelto the first pivot axis A1 and the second pivot axis A2. In thisembodiment, the rotational axis R is also parallel to the third pivotaxis A3 and the fourth pivot axis A4. The rotational axis R of theoutput shaft 64 and the first pivot axis A1 are coaxial in theillustrated embodiment. The output shaft 64 of the motor unit 24 drivesthe outer link 60 to move the movable member 20 with respect to the basemember 18. The inner link 62 moves in response to movement of the outerlink 60. Basically, a movement force of the output shaft 64 of the motorunit 24 is transmitted to the outer link 60 at the intermediate portion80 c, which is located between the first and second pivot axes A1 and A2of the outer link 60 by the saver mechanism 26.

Now the saver mechanism 26 will be discussed in more detail withreference to FIGS. 12 to 16. The saver mechanism 26 includes an outputmember 94, a drive link 96 and a biasing element 98. The saver mechanism26 basically performs two functions. First, the saver mechanism 26normally transmits a drive force of the motor 84 to the outer link 60for moving the movable member 20 with respect to the base member 18.Second, the saver mechanism 26 stops the transmission of a drive forceof the motor 84 to the outer link 60 such that the motor unit 84 cancontinue to operate even though the movable member 20 will not move withrespect to the base member 18 (e.g. becomes jammed), or the force tomove the movable member 20 with respect to the base member 18 becomesgreater than a prescribed operating force. In this way, the motor unit84 is protected by the saver mechanism 26 in certain situations.

As seen in FIGS. 15 to 16, the output member 94 is movably operated bythe motor 84 of the motor unit 24. In particular, the output member 94is fixed on the output shaft 64 of the motor unit 24 to rotate with theoutput shaft 64. For example, the output member 94 is fixed to theoutput shaft 64 of the motor unit 24 by a spline connection asillustrated. In this way, the output member 94 is turned as the outputshaft 64 of the motor unit 24 is turned by the operation of the motor84. The movement force (i.e., torque) of the output member 94 istransmitted by the drive link 96 to the outer link 60 at theintermediate portion 80 c of the first linking member 80, which islocated between the first and second pivot axes A1 and A2 of the outerlink 60. More specifically, the drive link 96 is movably mounted on theouter link 60 between a drive transmitting position that connects adrive force of the motor 84 to the outer link 60 and a non-drivetransmitting position that disconnect the drive force of the motor 84from the outer link 60. The biasing element 98 applies a biasing forceon the drive link 96 to bias the drive link 96 into contact with theoutput member 94. The drive link 96 engages the output member 94 to movetogether while the drive link 96 is in the drive transmitting position.On the other hand, the drive link 96 disengages from the output member94 to provide relative movement between the drive link 96 and the outputmember 94 while the drive link 96 is in the non-drive transmittingposition. The drive link 96 moves from the drive transmitting positionto the non-drive transmitting position upon a prescribed resistanceoccurring in the outer link 60, which overcomes the biasing force of thebiasing element 98 on the drive link 96.

As seen in FIGS. 15 to 16, the biasing element 98 applies a biasingforce on the drive link 96 to bias the drive link 96 into engagementwith the output member 94. Thus, the output shaft 64 of the motor unit24 is linked to the outer link 60 by the output member 94 and the drivelink 96 as a result of the biasing element 98 such that the drive forceof the motor 84 is transmitted to the outer link 60 for moving themovable member 20 with respect to the base member 18. The biasingelement 98 applies a biasing force on the drive link 96 into engagementwith the output member 94 to maintain the drive link 96 in the drivetransmitting position. Thus, this arrangement of the output member 94,the drive link 96 and the biasing element 98 for provides an overridableconnection between the output shaft 64 of the motor unit 24 and theouter link 60 in which the connection between the output shaft 64 of themotor unit 24 and the outer link 60 is switched from the drivetransmitting position to the non-drive transmitting position upon theforce required to move the movable member 20 with respect to the basemember 18 becoming greater than a prescribed operating force.

More specifically, in the illustrated embodiment, the drive link 96 ispivotally mounted to the second linking member 82 by a pivot pin 100that defines a pivot axis X. The drive link. 96 includes a contactportion 96 a that receives the biasing force of the biasing element 98and an output engagement portion 96 b that engages the output member 94to establish the drive transmitting position. The output engagementportion 96 b is located between the contact portion 96 a and the pivotaxis X where the drive link 96 is pivotally mounted on the secondlinking member 82. In the illustrated embodiment, the overridableconnection between the output shaft 64 of the motor unit 24 and theouter link 60 is established by providing one of the output engagementportion 96 b and the output member 94 with a notch and the other of theoutput engagement portion 96 b and the output member 94 with aprotrusion that mates with the notch to establish the drive transmittingposition. For example, as illustrated, the output member 94 includes anotch 94 a and the output engagement portion 96 b is a protrusion thatmates with the notch 94 a to establish the drive transmitting position.

In the illustrated embodiment, the biasing element 98 is a coil springthat is mounted on the mounting element 74 that attaches the secondlinking member 82 to the first linking member 80. In particular, thebiasing element 98 has a coil portion 98 a disposed on the mountingelement 74, a first end portion 98 b contacting the first linking member80 and a second end portion 98 c contacting the drive link 96. Asmentioned above, one end of the biasing member 72 is also connected tothe mounting element 74. Thus, the mounting element 74 performs severalfunctions to provide a compact arrangement with a minimal number ofparts.

FIGS. 7, 8, 15 and 16 illustrate situations in which the movable member20 will not move with respect to the base member 18 (e.g. becomesjammed), or for some reason the force to move the movable member 20 withrespect to the base member 18 becomes greater than a prescribedoperating force, which is determined by the biasing force of the biasingelement 98. If the movable member 20 becomes stuck, and the output shaft64 of the motor unit 2.4 is driven by the motor 84, the saver mechanism26 will permit the output shaft 64 of the motor unit 24 to rotate. Inparticular, the output member 94 will act as a cam that moves the drivelink 96 against the biasing force of the biasing element 98. Thismovement of the drive link 96 by the output member 94 against thebiasing force of the biasing element 98 results in the output engagementportion 96 b (e.g., protrusion) of the drive link 96 being forced out ofthe notch 94 a of the output member 94 and onto a cam surface 94 b ofthe output member 94. Once the output engagement portion 96 b is restingon the cam surface 94 b, the output shaft 64 of the motor unit 24 canrotate without transmitting the drive force to the outer link 60. Thecam surface 94 b of the output member 94 extends in both circumferentialdirections from the notch 94 a of the output member 94. in this way, themotor 84 is protected in both operating directions.

The term “connect” or “connected”, as used herein, encompassesconfigurations in which an element is directly secured to anotherelement by affixing the element directly to the other element;configurations in which the element is indirectly secured to the otherelement by affixing the element to intermediate member(s) which in turnare affixed to the other element; and configurations in which oneelement is integral with another element, i.e. one element is unitarypart of the other element. For example, the magnetized part can bedirectly secured to the crank arm attachment part, or can be indirectlysecured to the crank arm attachment part through intermediate member(s),or can be integral with the crank arm. attachment part. This definitionalso applies to words of similar meaning, for example, the terms“attach”, “attached”, “join”, “joined”, “fix”, “fixed”, “bond”,“bonded”, “couple”, “coupled ” and their derivatives.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. For example, the size, shape, location ororientation of the various components can be changed as needed and/ordesired so long as they do not substantially their intended function.Components that are shown directly connected or contacting each othercan have intermediate structures disposed between them unlessspecifically stated otherwise. The functions of one element can beperformed by two, and vice versa unless specifically stated otherwise.The structures and functions of one embodiment can be adopted in anotherembodiment. It is not necessary for all advantages to be present in aparticular embodiment at the same time. Every feature which is uniquefrom the prior art, alone or in combination with other features, alsoshould be considered a separate description of further inventions by theapplicant, including the structural and/or functional concepts embodiedby such feature(s). Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed is:
 1. A bicycle rear derailleur comprising: abusemember configured to be mounted to a bicycle frame, the base memberhaving a frame facing side and a non-frame facing side; a movable membermovably coupled to the base member; a linkage including an outer linkpivotally connected to the base member about a first pivot axis andpivotally connected to the movable member about a second pivot axis, andan inner link pivotally connected the base member about a third pivotaxis and the movable member about a fourth pivot axis, the first,second, third and fourth pivot axes being offset from each other, theouter link overlying the inner link as viewed from a direction facingthe frame facing side of the base member; and a motor unit including anoutput shaft having a rotational axis being parallel to at least one ofthe first pivot axis and the second pivot axis, the output shaft of themotor unit being configured to pivotally support the outer link, theoutput shaft of the motor unit driving the outer link such that a motorforce is transmitted from the outer link to the inner link to move themovable member with respect to the base member, the inner link moving inresponse to movement of the outer link.
 2. The bicycle rear derailleuraccording to claim 1, wherein a movement force of the output shaft ofthe motor unit is transmitted at a portion of the outer link locatedbetween the first and second pivot axes of the outer link.
 3. Thebicycle rear derailleur according to claim 1, wherein the rotationalaxis of the output shaft and the first pivot axis are coaxial.
 4. Thebicycle rear derailleur according to claim 1, wherein the linkageincludes a biasing member interposed between the inner link and theouter link to bias the movable member to one of a low shift stageposition and a top shift stage position.
 5. The bicycle rear derailleuraccording to claim 1, further comprising a saver mechanism isoperatively coupled between the output shaft of the motor unit and theouter link.
 6. The bicycle rear derailleur according to claim 5, whereinthe outer link includes a first linking member pivotally connected tothe movable member, and a second linking member pivotally connected tothe base member and being attached to the first linking member; and thesaver mechanism includes an output member movably operated by the motorunit, a drive link movably mounted on the outer link between a drivetransmitting position that connects a drive force of the motor to theouter link and a non-drive transmitting position that disconnect thedrive force of the motor from the outer link, and a biasing elementapplying a biasing force on the drive link into engagement with theoutput member to maintain the drive link in the drive transmittingposition.
 7. The bicycle rear derailleur according to claim 6, whereinthe biasing element is mounted on a mounting element that attaches thesecond linking member to the first linking member.
 8. The bicycle rearderailleur according to claim 7, further comprising a biasing memberhaving a first end connected to the mounting element and a second endconnected to the inner link.
 9. The bicycle rear derailleur according toclaim 7, wherein the biasing element is a coil spring having a coilportion disposed on the mounting element and a first end portioncontacting the first linking member and a second end portion contactingthe drive link.
 10. The bicycle rear derailleur according to claim 6,wherein the drive link is pivotally mounted on the second linkingmember.
 11. The bicycle rear derailleur according to claim 6, whereinthe second linking member is rotatably mounted on the output shaft ofthe motor unit.
 12. The bicycle rear derailleur according to claim 11,wherein the output member is fixed on the output shaft of the motor unitto rotate with the output shaft.
 13. The bicycle rear derailleuraccording to claim 1, further comprising a chain guide pivotally coupledto the movable member about a chain guide pivot axis; and a frictionelement operatively arranged between the movable member and the chainguide to frictionally provide rotational resistance in a firstrotational direction of the chain guide about the chain guide pivotaxis.
 14. A bicycle rear derailleur comprising: a base member configuredto be mounted to a bicycle; a movable member movably coupled to the basemember; a linkage including an outer link pivotally connected to thebase member about a first pivot axis and pivotally connected to themovable member about a second pivot axis, and an inner link pivotallyconnected the base member about a third pivot axis and the movablemember about a fourth pivot axis, the first, second, and third pivotaxes being offset from each other; a motor unit including an outputshaft having a rotational axis being parallel to at least one of thefirst pivot axis and the second pivot axis, the output shaft of themotor unit being configured to pivotally support the outer link, theoutput shaft of the motor unit driving the outer link to move themovable member with respect to the base member such that a motor forceis transmitted from the outer link to the inner link, the inner linkmoving in response to movement of the outer link; a drive link pivotallymounted on an axis offset from the rotational axis of the output shaft;and a biasing element interposed between the outer link and the drivelink to apply a biasing force on the drive link.
 15. A bicycle rearderailleur comprising: a base member configured to be mounted to abicycle; a movable member movably coupled to the base member; a linkageincluding an outer link pivotally connected to the base member about afirst pivot axis and pivotally connected to the movable member about asecond pivot axis, and an inner link pivotally connected the base memberabout a third pivot axis and the movable member about a fourth pivotaxis, the first, second, third and fourth pivot axes being offset fromeach other; and a motor unit including an output shaft having arotational axis being parallel to at least one of the first pivot axisand the second pivot axis, the outer link being fixed to the outputshaft of the motor unit, the output shaft of the motor unit beingconfigured to pivotally support the outer link, the output shaft drivingthe outer link to move the movable member with respect to the basemember such that a motor force is transmitted from the outer link to theinner link, the inner link moving in response to movement of the outerlink.